stanley miller harold urey experiment

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Miller-Urey Experiment

The Miller-Urey Experiment was a landmark experiment to investigate the chemical conditions that might have led to the origin of life on Earth. The scientist Stanley Miller, under the supervision of the Nobel laureate scientist Harold Urey conducted it in 1952 at the University of Chicago. They tried to recreate the conditions that could have existed in the first billion years of the Earth’s existence (also known as the Early Earth) to check the said chemical transformations.

Miller-Urey Experiment And The Primordial Soup Theory

The experiment tested the primordial or primeval soup theory developed independently by the Soviet biologist A.I. Oparin and English scientist J.B.S. Haldane in 1924 and 1929 respectively. The theory propounds the idea that the complex chemical components of life on Earth originated from simple molecules occurring naturally in the reducing atmosphere of the Early Earth, sans oxygen. Lightning and rain energized the said atmosphere to create simple organic compounds that formed an organic “soup”. The so-called soup underwent further changes giving rise to more complex organic polymers and finally life.

The Miller-Urey Experiment In Support Of Abiogenesis

From what was explained in the previous paragraph, it can undoubtedly be considered as a classic experiment to demonstrate abiogenesis. For those who are not conversant with the term, abiogenesis is the process responsible for the development of living beings from non-living or abiotic matter. It is thought to have taken place on the Earth about 3.8 to 4 billion years ago.

Miller-Urey Experiment Apparatus and Procedure

The groundbreaking experiment used a sterile glass flask of 5 liters attached with a pair of electrodes, to hold water (H 2 O), methane (CH 4 ), ammonia (NH 3 ) and hydrogen (H 2 ), the major components of primitive Earth. This was connected to another glass flask of 500 ml capacity half filled with water. On heating it, the water vaporized to fill the larger container with water vapor. The electrodes induced continuous electrical sparks in the gas mixture to simulate lightning. When the gas was cooled, the condensed water made its way into a U-shaped trap at the base of the apparatus.

After electrical sparking had continued for a day, the solution in the trap turned pink in color. At the end of a week, the boiling flask was removed, and mercuric chloride added to prevent microbial contamination. After stopping the chemical reaction, the scientist duo examined the cooled water collected to find that 10-15% of the carbon present in the system was in the form of organic compounds. 2% of carbon went into the formation of various amino acids, including 13 of the 22 amino acids essential to make proteins in living cells, glycine being the most abundant.

Though the result was the production of only simple organic molecules and not a complete living biochemical system, still the simple prebiotic experiment could, to a considerable extent, prove the primordial soup hypothesis.

Miller-Urey Experiment Animation

Chemistry of the miller and urey experiment.

The components of the mixture can react among themselves to produce formaldehyde (CH 2 O), hydrogen cyanide (HCN) and other intermediate compounds.

CO 2 → CO + [O] (atomic oxygen)

CH 4 + 2[O] → CH 2 O + H 2 O

CO + NH 3 → HCN + H 2 O

CH 4 + NH 3 → HCN + 3H 2

The ammonia, formaldehyde and HCN so produced react by a process known as Strecker synthesis to form biomolecules including amino acids.

CH 2 O + HCN + NH 3 → NH 2 -CH 2 -CN + H 2 O

NH 2 -CH 2 -CN + 2H 2 O → NH 3 + NH 2 -CH 2 -COOH (glycine)

In addition to the above, formaldehyde and water can react by Butlerov’s reaction to produce a variety of sugars like ribose, etc.

Though later studies have indicated that the reducing atmosphere as replicated by Miller and Urey could not have prevailed on primitive Earth, still, the experiment remains to be a milestone in synthesizing the building blocks of life under abiotic conditions and not from living beings themselves.

https://www.bbc.co.uk/bitesize/guides/z2gjtv4/revision/1

https://www.juliantrubin.com/bigten/miller_urey_experiment.html

Article was last reviewed on Thursday, February 2, 2023

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One response to “Miller-Urey Experiment”

This experiment is currently seen as not sufficient to support abiogenesis. See Stephen C. Meyer, James Tour.

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• Biology Article

Miller Urey Experiment

Miller and urey experiment.

Stanley L. Muller and Harold C. Urey performed an experiment to describe the origin of life on earth. They were of the idea that the early earth’s atmosphere was able to produce amino acids from inorganic matter. The two biologists made use of methane, water, hydrogen, and ammonia which they considered were found in the early earth’s atmosphere. The chemicals were sealed inside sterile glass tubes and flasks connected together in a loop and circulated inside the apparatus.

One flask is half-filled with water and the other flask contains a pair of electrodes. The water vapour was heated and the vapour released was added to the chemical mixture. The released gases circulated around the apparatus imitating the earth’s atmosphere. The water in the flask represents the water on the earth’s surface and the water vapour is just like the water evaporating from lakes, and seas. The electrodes were used to spark the fire to imitate lightning and storm through water vapour.

The vapours were cooled and the water condensed. This condensed water trickles back into the first water flask in a continuous cycle. Miller and Urey examined the cooled water after a week and observed that 10-15% of the carbon was in the form of organic compounds. 2% of carbon had formed 13 amino acids . Yet, the Miller and Urey experiments were condemned by their fellow scientists.

Also read: Origin Of Life

Criticism of the Miller Urey Experiment

The experiment failed to explain how proteins were responsible for the formation of amino acids. A few scientists have contradicted that the gases used by Miller and Urey are not as abundant as shown in the experiment. They were of the notion that the gases released by the volcanic eruptions such as oxygen, nitrogen, and carbon dioxide make up the atmosphere. Therefore, the results are not reliable.

Oparin and Haldane

In the early 20th century, Oparin and Haldane suggested that if the atmosphere of the primitive earth was reducing and if it had sufficient supply of energy such as ultraviolet radiations and lightning, organic compounds would be synthesized at a wide range.

Oparin believed that the organic compounds would have undergone a series of reactions to form complex molecules. He suggested that the molecules formed coacervates in the aqueous environment.

Haldane proposed that the atmosphere of the primordial sea was devoid of oxygen, and was a composed of ammonia, carbon dioxide, and ultraviolet light. This gave rise to a host of organic compounds. The sea contained large amounts of organic monomers and polymers, and the sea was called a ‘hot dilute soup’. He conceived that the polymers and monomers acquired lipid membranes. The molecules further developed and gave rise to the first living organism. ‘Prebiotic soup’ was the term coined by Haldane.

Also read: Evolution of Life on Earth

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Miller-Urey Experiment – Definition & Detailed Explanation – Astrobiology Glossary

Table of Contents

What is the Miller-Urey Experiment?

The Miller-Urey Experiment is a groundbreaking scientific experiment that was conducted in 1953 by chemists Stanley Miller and Harold Urey. The experiment aimed to simulate the conditions of early Earth in order to investigate the origins of life. This experiment is considered one of the most important in the field of astrobiology and has had a significant impact on our understanding of the origins of life on Earth.

How was the Miller-Urey Experiment conducted?

In the Miller-Urey Experiment, Stanley Miller and Harold Urey created a closed system that mimicked the conditions of early Earth’s atmosphere. They used a mixture of gases such as methane, ammonia, hydrogen, and water vapor, which were believed to be present in the atmosphere of early Earth. The gases were circulated through a series of glass tubes and flasks, representing the oceans and atmosphere of the early Earth.

The gases were then subjected to electrical sparks to simulate lightning, which was thought to be a common occurrence in the early Earth’s atmosphere. After running the experiment for a week, Miller and Urey observed that the mixture of gases had produced a variety of organic compounds, including amino acids, which are the building blocks of proteins and essential for life.

What were the key findings of the Miller-Urey Experiment?

The key findings of the Miller-Urey Experiment were groundbreaking in the field of astrobiology. The experiment demonstrated that under the conditions of early Earth, simple organic molecules could spontaneously form from inorganic compounds. This provided evidence that the basic building blocks of life could have originated on Earth through natural processes.

The experiment also showed that the formation of complex organic molecules, such as amino acids, could occur in a relatively short period of time. This suggested that the origins of life may not have required millions of years, but could have happened relatively quickly under the right conditions.

What impact did the Miller-Urey Experiment have on the field of Astrobiology?

The Miller-Urey Experiment had a profound impact on the field of astrobiology. It provided experimental evidence to support the theory that life could have originated on Earth through natural processes. The experiment sparked further research into the origins of life and the conditions that may have existed on early Earth.

The findings of the Miller-Urey Experiment also inspired scientists to explore the possibility of life on other planets. By demonstrating that the basic building blocks of life could form under conditions similar to those found on early Earth, the experiment raised the possibility that life could exist elsewhere in the universe.

How has the Miller-Urey Experiment influenced our understanding of the origins of life on Earth?

The Miller-Urey Experiment has significantly influenced our understanding of the origins of life on Earth. The experiment provided evidence that the basic building blocks of life could have formed through natural processes on early Earth. This has led scientists to consider the possibility that life may be a common occurrence in the universe, given the right conditions.

The findings of the Miller-Urey Experiment have also led to further research into the origins of life and the conditions that may have existed on early Earth. Scientists continue to study the chemical reactions that could have led to the formation of complex organic molecules, with the goal of understanding how life first emerged on our planet.

What are some criticisms of the Miller-Urey Experiment?

While the Miller-Urey Experiment was groundbreaking in its findings, it has also faced criticism from some scientists. One criticism is that the experiment may not accurately reflect the conditions of early Earth’s atmosphere. Some researchers argue that the gases used in the experiment were not representative of the actual composition of the early Earth’s atmosphere.

Another criticism is that the experiment may have produced a higher concentration of organic compounds than would have been present on early Earth. Some scientists believe that the conditions of the experiment were too idealized and may not have accurately reflected the complexity of the early Earth environment.

Despite these criticisms, the Miller-Urey Experiment remains a landmark study in the field of astrobiology. It has paved the way for further research into the origins of life and has inspired scientists to explore the possibility of life beyond Earth. The experiment continues to be studied and referenced in scientific literature, as researchers seek to unravel the mysteries of how life first began on our planet.

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Miller-Urey Experiment

• Last Updated: May 10, 2023

Stanley Miller and Harold Urey in 1953 tested the Oparin-Haldane Theory and were successful in producing the organic molecules from some inorganic compounds which were thought to be present at the time of pre – biotic earth; this experiment is known as Miller-Urey experiment.

Water vapour, methane, ammonia, and molecular hydrogen were mixed with warm water, and the created atmosphere was then stimulated with electrical charges. The various elements were designed to represent, respectively, the early ocean, the early atmosphere, and heat (in the shape of lightning). One week later Miller and Urey found that simple organic molecules, including amino acids (the building blocks of proteins), had formed under the simulated conditions of early Earth.

The experiment

The apparatus included a spark chamber with two electrodes (to simulate lightning), a boiling flask (to simulate evaporation and circulation), and a condenser (to simulate raining and Haldane’s soup). A control apparatus, but without electrodes in the spark chamber, was also prepared. Miller employed a combination of methane, ammonia, hydrogen, and water. The mixture was subjected to electric discharges, which were followed by condensation and boiling. . It continued for a total of 18 days more. There were several runs of the trial. The compounds were extracted and identified using chromatography. Chromatography was used to extract and identify and analyse the compounds. Miller identified 15 amino acids (like, glycine, alanine, aspartic acid, glutamic acid), organic acids (like, lactic acid, succinic acid, propionic acid, acetic acid), a ribose sugar, and purine adenine.

The sensors are in the other flask, which has half as much water as the first. The chemical mixture received the heated water vapour after it had been introduced to it. The apparatus was surrounded by swirling gases that replicated the Earth’s atmosphere. While the water vapour symbolises water evaporating from lakes and seas, the water in the flask represents water on the earth’s surface. The electrodes were used to start the fire in order to mimic lighting and a storm using water vapour as a medium. Water collected as the vapours cooled. In a continuous loop, the condensed water goes back to the first water flask. After a week, Miller and Urey looked at the chilled water and found that 10-15% of the carbon was in the form of carbon dioxide.

Significance of Miller-Urey Experiment

• It represents a major advance in the study of the origin of life.
• Even though the details of the origin of life have been changed, the first stage was chemical evolution, which was proved by Miller and Urey.
• The experiment laid a groundwork for further studies.
• The basic result i.e. organic molecules formed from inorganic matter are still valid.
• The electrical discharges produced during lightning in the primitive earth’s atmosphere, which contained hydrogen, ammonia, nitrogen, and water vapour, could have resulted in the formation of amino acids and other essential building blocks (Sugars, Nucleotides, and so on) of living organisms.
• The Miller and Urey experiment provided support for Oparin and Haldane’s biochemical theory of life’s origin.
• Miller and Urey’s experiment shows that it is possible to transition from the inorganic to the biological organic level.
• It also demonstrates that life in the ocean began at the molecular level and progressed to the cellular level. The abiotic synthesis of organic molecules is demonstrated in this experiment.

Criticism of Miller-Urey Experiment

• The experiment fell short of explaining how proteins were in charge of creating amino acids. 
• Some experts disagree, claiming that the gases used by Miller and Urey are not as prevalent as the experiment indicates. They held that gases like oxygen, nitrogen, and carbon dioxide are released during volcanic explosions and make up the atmosphere. The outcomes are therefore unreliable.
• The experiment lacked larger macromolecules like proteins and DNA that are essential for living.
• To reduce the risk of contamination, intricate tests should be conducted in a sealed, inert, and sterilised environment. Miller, however, used a glass device to conduct his experiment. In the experimental broth, the borosilicate glass roughly disintegrated and altered the amount of amino acids produced, which is not observed when experiments are conducted in teflon equipment.
• The main idea was that the primitive earth’s conditions were only hypothesised and might not be true.

Abiogenesis and Miller-Urey Experiment 

The Oparin-Haldane theory and the Miller-Urey experiment share many of the same foundational ideas with contemporary abiogenesis theories. The various models that have been proposed to explain the development from abiogenic molecule to living organism do, however, differ slightly, and explanations differ as to whether complex organic molecules first became self-replicating entities lacking metabolic functions or first became metabolising protocells that then developed the ability to self-replicate.

Organic molecules can form from abiogenic materials under the constraints of Earth’s prebiotic atmosphere, as demonstrated by the Miller-Urey experiment.

Analysis in meteorite content also revealed similar kinds of compounds indicating similar processes are occurring in space as well. The chemical evolution part of Miller-Urey conjecture was accepted.

• Rogers, K. (2023, February 15). Abiogenesis . Encyclopedia Britannica. https://www.britannica.com/science/abiogenesis . Accessed on 04 March 2023.
• Gishlick Alan. Icons of Evolution? Why Much of What Jonathan Wells Writes about Evolution is wrong. National Center for Science Education. https://ncse.ngo/files/pub/creationism/icons/gishlick_icons1.pdf . Accessed on 04 March 2023.
• Parker, E. T., Cleaves, J. H., Burton, A. S., Glavin, D. P., Dworkin, J. P., Zhou, M., Bada, J. L., & Fernández, F. M. (2014). Conducting miller-urey experiments. Journal of visualized experiments : JoVE , (83), e51039. https://doi.org/10.3791/51039 . Accessed on 04 March 2023.
• Miller SL. Production of Some Organic Compounds under Possible Primitive Earth Conditions. J. Am. Chem. Soc. 1955;77:2351–2361.

Shefali Sharma is a Research Scholar in the Department of Anthropology at University of Rajasthan. She obtained a prestigious meritorious award by University of Rajasthan in 2022. She also holds qualifications such as UGC – NET. She is a writer by the day and reader by the night and has worked as a content writer for various websites.

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Harold Urey and the famous Miller–Urey experiment

Harold Urey (1893-1981)

On April 29 , 1893 ,  American physical chemist and Nobel Laureate  Harold C. Urey was born. He played a significant role in the development of the atom bomb , but may be most prominent for his contribution to theories on the development of organic life from non-living matter .

Harold Urey – Early Years

Harold Clayton Urey entered the University of Montana in 1914 and received his Bachelor of Science degree in Zoology in 1917 . A few years later, he returned to Montana as an instructor in Chemistry and entered the University of California to work under Professor Lewis in 1921 . Urey was awarded the degree of Ph.D. in Chemistry in 1923 . Urey later worked in Copenhagen at Professor Niels Bohr’s Institute for Theoretical Physics as American-Scandinavian Foundation Fellow to Denmark and on his return to the United States he became an Associate in Chemistry at Johns Hopkins University . Urey became professor in Chemistry at Columbia University in the 1930s and moved to the Institute for Nuclear Studies, University of Chicago in 1945 as Distinguished Service Professor of Chemistry . In 1958 , he took his post as Professor-at-Large, University of California . During the Second World War, he and his team worked on various research projects within the Manhattan Project, thus contributing to the development of the first atomic bomb. The most significant of these was the development of the gas diffusion process for the separation of 235 U and 238 U. Urey was an early opponent of German Nazism and assisted refugee scientists, including Enrico Fermi , by helping them find work in the United States, and to adjust to life in a new country.

Miller–Urey experiment

The Miller Urey Experiment

Space exploration.

In the late 1950s and early 1960s, space science became a topical field of research in the wake of the launch of Sputnik I .[ 5 ] Urey helped persuade NASA to make unmanned probes to a moon a priority. When Apollo 11 returned moon rock samples from the moon, Urey examined them at the Lunar Receiving Laboratory. The samples supported Urey’s contention that the moon and the Earth shared a common origin.  Lunar astronaut  Harrison Schmitt  said that Urey approached him as a volunteer for a one-way mission to the Moon, stating “ I will go, and I don’t care if I don’t come back.”

Nobel Prize in Chemistry

Apart from his Nobel Prize in Chemistry , Harold Urey was also awarded the Willard Gibbs Medal , the Davy Medal , the Medal of Merit, and many more. He is author of many books including Atoms , Molecules and Quanta , published in 1930 . Urey was editor of the  Journal of Chemical Physics during 1933-1940 and has written numerous papers on the structure of atoms and molecules , the discovery of heavy hydrogen and its properties , separation of isotopes , measurement of paleotemperatures and the origin of planets . These have been published in many different chemical journals . In 1928 he became a Fellow of the American Physical Society. Since 1935 he was a member of the National Academy of Sciences. In 1938 he was elected to the American Academy of Arts and Sciences. In 1947 he was elected a Foreign Member of the Royal Society. In 1940 he received the Davy Medal and in 1964 the National Medal of Science.

Harold Urey died on January 5, 1981 , at age 87.

References and Further Reading:

• [1] Harold Urey at the Official Website of the Nobel Prize
• [2]  Voice Interview with Harold Urey
• [3]  Harold Urey Life and Work
• [4]  Stanley Miller’s Landmark Experiment on the Origin of Life , SciHi Blog
• [5]  The Sputnik Shock , SciHi Blog
• [6] Harold Urey at Wikidata
• [7]  Silverstein, Alvin; Silverstein, Virginia B. (1970).  Harold Urey: the Man who Explored from Earth to Moon . New York: J. Day. 
• [8]  National Academy of Sciences biography
• [9]  1965 Audio Interview with Harold Urey by Stephane Groueff   Voices of the Manhattan Project
• [10]  Harold C. Urey:  The thermodynamic properties of isotopic substances . In:  Journal of the Chemical Society (Resumed) . 1947, S. 562.
• [11]  Miller-Urey Experiment | Chemical Evolution | Bio 101 | STEMstream , STEMstream @ youtube
• [12] Timeline of Nobel Laureates in Chemistry , via Wikidata

Tabea Tietz

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